Studies in detoxication: The metabolism of vanillin and vanillic acid in the rabbit. The identification of glucurovanillin and the structure of glucurovanillic acid.

WHEN aldehydes are fed to animals, the -CHO group is either reduced to -CH20H or oxidized to -COOH. It can be stated broadly that those aldehydes undergoing biological reduction are aliphatic in nature, whilst those oxidized to the corresponding acid are aromatic.2 Examples of the former are chloral [Musculus & Mering, 1875; Mering, 1882], butyl chloral [Mering, 1882] and bromal [Maraldi, 1903]. Besides these halogenated derivatives few other aliphatic aldehydes have been studied although Neubauer [1901] states that he could not detect conjugated glucuronic acid in the urine of dogs and rabbits after feeding isobutaldehyde, isovaleraldehyde and heptaldehyde; Cohn [1893] was also unable to detect any metabolic products after acetaldehyde and paraldehyde. These aldehydes probably undergo complete oxidation in vivo, since Boyland [1940] has recently stated that heptaldehyde appears to be completely oxidized in the rabbit, as he was unable to detect any of its possible metabolic products (heptyl alcohol, heptoic and pimelic acids) in the urine. Aromatic aldehydes without exception are oxidized to the corresponding acids, e.g. benzaldehyde, substituted benzaldehydes, thiophene aldehyde [Cohn, 1893] and p-nitrophenylacetaldehyde [Sherwin & Hynes, 1921]. Furfuraldehyde also behaves as an aromatic aldehyde, but, unlike the others, it forms in dogs and rabbits (but not in hens) small amounts of furfuracrylic acid which is excreted in conjugation with glycine [Jaffe & Cohn, 1887; 1888; Cohn, 1893]. The open chain terpene aldehyde, citral (geranial) has its -CHO group oxidized to -COOH in vivo [Kuhn et al. 1936], but the closely related aldehyde, citronellal, deserves special mention since it is cyclized in the rabbit, forming a menthoglycol, and it appears that ring formation takes place in the stomach under the influence of thq gastric HCI [Kuhn & Low, 1938]. The metabolism of vanillin